Master thesis presentation in Physics. The thesis title is "Secondary Electron Emission of Anions and Photodetachment Studies".
Ilse Kardasch
Negative ions, or neutral atoms with an additional weakly bound electron, are studied to gain insights into various phenomena in the universe, as they are present in space, the atmosphere, and numerous chemical processes. One property of interest is the electron affinity (EA), defined as the energy gained by a neutral atom when an anion is formed. There are different methods to measure the EA, however laser photodetachment threshold spectroscopy (LPTS) allows to obtain the EA of a p-wave
photodetachment and, with a higher precision, the value of an s-wave photodetachment. LPTS uses neutral particle detectors (NPD) to determine the cross sections of electron affinities. NPDs operate based on secondary electron emission (SEE), which occurs when a neutral atom collides with a target plate, causing electron emission.
This thesis centers on three experiments. The first experiment involved a campaign to determine the absolute detection efficiency of the NPD used at a research facility called GUNILLA, aimed at enabling measurements of the absolute cross sections of hydrogen (H) and deuterium (D) for applications in plasma heating in fusion reactors. In this experiment, a setup was designed to characterize secondary electron emission as a function of the mass and kinetic energy of anions used as projectiles, and two different target materials were analyzed: one with a low work function and another with a higher work function. The second experiment, conducted at the DESIREE facility, focused on using a newly developed LPTS method to achieve a high-precision measurement of the electron affinity of the silicon anion and its stable isotopes. The final experiment provided a preliminary value for the binding energy of the excited state of the tungsten negative ion. Describing the tungsten anion is of interest because it provides insight into this inherently complex atom, which involves intricate theoretical calculations.
Supervisor: David Leimbach
Examinator: Dag Hanstorp
Opponent: Willem Vanmoerkerke
Monday 3 June at 13.00 in Nexus